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Graphene-on-glass advances semiconductors

Posted: 13 Feb 2016 ?? ?Print Version ?Bookmark and Share

Keywords:graphene? graphene technology? doping?

Graphene has long been heralded as a breakthrough "wonder material" for its extreme durability, electrical conductivity and transparency into a one-atom-thick sheet of carbon. However, this two-dimensional powerhouse has yet to penetrate the commercial and industrial products and process.

A group of scientists have employed a new method that helps create resilient, customised and high performing graphene: layering it on top of common glass. This scalable and inexpensive process helps pave the way for a new class of microelectronic and optoelectronic devices!everything from efficient solar cells to touch screens.

The collaboration!led by scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory, Stony Brook University (SBU), and the Colleges of Nanoscale Science and Engineering at SUNY Polytechnic Institute!published their results February 12, 2016, in the journal Scientific Reports.

According to physicist at Brookhaven Lab and study coauthor Matthew Eisaman, the new development could greatly advance graphene technologies.

Scientists conducting preliminary tests

Study co-author performing high-resolution electron microscopy measurements at the Centre for Functional Nanomaterials.(Image source: Brookhaven National Laboratory)

The scientists built the proof-of-concept graphene devices on substrates made of soda-lime glass!the most common glass found in windows, bottles, and many other products. In an unexpected twist, the sodium atoms in the glass had a powerful effect on the electronic properties of the graphene.

"The sodium inside the soda-lime glass creates high electron density in the graphene, which is essential to many processes and has been challenging to achieve," said coauthor Nanditha Dissanayake of Voxtel, Inc., but formerly of Brookhaven Lab. "We actually discovered this efficient and robust solution during the pursuit of something a bit more complex. Such surprises are part of the beauty of science."

Crucially, the effect remained strong even when the devices were exposed to air for several weeks!a clear improvement over competing techniques.

The experimental work was done primarily at Brookhaven's Sustainable Energy Technologies Department and the Centre for Functional Nanomaterials (CFN), which is a DOE Office of Science User Facility.

The graphene tweaks in question revolve around a process called doping, where the electronic properties are optimised for use in devices. This adjustment involves increasing either the number of electrons or the electron-free "holes" in a material to strike the perfect balance for different applications. For successful real-world devices, it is also very important that the local number of electrons transferred to the graphene does not degrade over time.

"The graphene doping process typically involves the introduction of external chemicals, which not only increases complexity, but it can also make the material more vulnerable to degradation," Eisaman said. "Fortunately, we found a shortcut that overcame those obstacles."

image name

Left: Schematic of a graphene field-effect-transistor used in this study. Right: A scanning electron micrograph of the device as seen from above, with the white scale bar measuring 10 microns. (Image source: Brookhaven National Laboratory)

The team initially set out to optimise a solar cell containing graphene stacked on a high-performance copper indium gallium diselenide (CIGS) semiconductor, which in turn was stacked on an industrial soda-lime glass substrate.

The scientists then conducted preliminary tests of the novel system to provide a baseline for testing the effects of subsequent doping. But these tests exposed something strange: the graphene was already optimally doped without the introduction of any additional chemicals.

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